1. Field of the Invention
The present invention relates to a buckle for securely fastening, for example, a belt, a tape or a string; an injection molding die; and an injection molding method, specifically to a manufacturing die for a plastic molding article having an undercut.
2. Description of Related Art
Fastening by a strip-shaped material such as a belt and a tape is often used in garments, bags, helmets, baby carriages, sporting goods and the like. In the fastening, a buckle that is attached to, for example, a belt and can be manually locked/unlocked is used.
Typically, the buckle has a plug (male member) and a socket (female member) and is locked by inserting the plug in the socket to a certain state.
Such typical buckle consists of the socket having a cylindrical shape; the plug to be inserted in the socket; and a lock mechanism for holding the socket and the plug in engagement.
The socket has a belt-holding part, or an attachment part to be fixed to a sheet and the like; and an insertion opening defined on a plug side.
The plug has a belt-holding part on one end; and a pair of lock arms on the other end, the lock arms extending in a direction to be engaged with the socket.
The lock arm is made of a flexible material and provided with an step-like engaging part in an outer surface thereof so as to be engageable with an inner surface of the socket.
The socket is provided with operation openings in both lateral surfaces thereof, which are for operating the lock arms from outside to release the engagement. A peripheral portion of the operation opening is used as an engaging part inside the socket, as stated above.
With this structure, when the plug is inserted in the socket, the lock arms are engaged with the inner surface of the socket to establish the engagement of the buckle. From this engagement state, the engagement between the pair of lock arms and the inner surfaces of the socket can be released by pinching the lock arms of the plug with fingers to press the lock arms inward, thereby easily dissolving the engagement of the buckle. Such type of buckle is called a side-release buckle, a side-push buckle or the like.
A buckle disclosed in the document 1 (Japanese Utility Model Publication No. 4-84581) has the operation opening defined in part of a surface, so that the engagement thereof can be released by pressing the lock arm of the plug through the opening.
Since this type of buckle can be released only by the pressing, the dissolving operation is simple. However, a user should be careful, as the buckle can be unintentionally released by error.
In a buckle disclosed in the document 2 (Japanese Patent Laid-Open Publication No. 2003-299519), the socket has the operation openings defined in both lateral surfaces thereof, and the plug has the pair of lock arms. Accordingly, the engagement of the buckle can be released by pinching the lock arms of the plug from the lateral sides.
This type of buckle requires the pinching operation on the pair of lock arms, thereby preventing an erroneous operation thereon.
In these buckles, a step face of the engaging part of the lock arm is a slant surface slanted toward the side opposite to an inserting direction as becoming closer to a tip end thereof, while a step face of the engaging portion of the socket is a slant surface slanted toward the inserting direction as becoming closer to a tip end thereof. Due to the slant, the engaging parts are displaced so as to more firmly engage with each other when the plug and the socket in engagement are pulled apart in a release direction, thereby preventing the plug from being pulled out of a socket (see, for example, the document 3: Japanese Patent Laid-Open Publication No. H10-57114).
The above described buckle is used not only for coupling belt ends, but also as a sheet attachment buckle for fixing a belt on an upper surface of an article or for closing a flap to cover an opening of a bag.
In such sheet attachment buckle, the socket or the plug is disposed on the upper side of the sheet, and an attachment member is disposed on a rear side of the sheet. The sheet is sandwiched by fixing the attachment member to the socket or the plug (see, for example, the document 4: Japanese Patent Laid-Open Publication No. 2004-329723).
In the above described sheet attachment buckle, the lock arms may be pressed on the sheet (in a second direction) when pinching the lock arms to release the engagement, the sheet being the article to which the buckle is attached.
Also in the buckle for coupling the belt ends, when handling with one hand, the buckle may be pressed on an upper side of another article during the pinching operation on both lateral surfaces.
To help the release operation including the pressing i.e. the operation in a first direction including the movement in the second direction, a buckle is manufactured such that the middle portion of the lock arm has a cross section with a slant intersecting both of the first direction and the second direction (see, for example, the document 5: Japanese Patent Publication No. 3494588).
When the above described sheet attachment buckle is used for a bag and the like, the socket may be disposed along the upper surface of the bag, so that the plug may often be inserted aslant in the socket. In order to stabilize the insert with a slant, the buckle having a guide bar is produced.
A buckle disclosed in the document 6 (U.S. Pat. No. 495,971) has the lock arm and the guide bar to facilitate the insertion of the plug in the socket. With the guide bar, the socket can be smoothly inserted by placing the guide bar at the opening of the socket while slanting the plug relative to the socket and moving the guide bar along the axial direction.
A plastic molding article such as the buckle is manufactured by injection molding.
In a typical injection molding, a movable die is moved to and closes with a fixed die, molten synthetic resin material is molded in a cavity, and the movable die is opened to remove the molding article.
In such typical injection molding, a concave or a convex in the molding article can be easily formed in an opening/closing direction of the die, but a concave or a convex (undercut) in a direction intersecting the opening/closing direction is difficult to form. This is because the undercut can be interfered when opening the die, interfering with a smooth removal of the molding article.
To solve this problem, a die is provided with a slide core that is advanceable and retractable to the fixed die or the movable die in order to form the undercut with the slide core (see, for example, the document 7: Japanese Patent Publication No. 2003-311791 and the document 8: No. H9-300362).
In the buckle of the document 5, to handle the operation in the first direction including the operation in the second direction and to obtain the pull-out prevention effect due to the slant, the engaging part of the lock mechanism of the lock arm or the socket employs two hook surfaces corresponding to the first and second directions.
Specifically, a first hook surface is provided to a portion near the front and rear surfaces of the socket out of the peripheral of the operation opening of the socket, while a second hook surface is provided to a portion near the lateral surfaces of the socket.
The two hook surfaces are formed in directions orthogonal to each other. A slant similar to the slant of the document 3 is formed to obtain the pull-out prevention effect in the first and second directions.
In the arrangement in which the two hook surfaces have a slant in the first direction and second direction, it has been desired to improve engaging force of the engaging portion and to achieve a smooth and easy operation even in the release operation including the pressing.
The guide bar of the document 6 has the front and rear surface recessed in the middle portion in an arc shape (a direction of the thickness of the buckle), so that the middle portion is prevented from interfering with the opening of the socket even when the plug is inserted aslant relative to the socket.
However, the guide bar with the middle portion being recessed slidably contact the inner surface of the socket only at a tip end of the guide bar, there has been desired an arrangement that can more reliably provide the stability in the postures of the socket and the plug in engagement.
In the documents 7 and 8, the slide core projecting in the cavity is used. The slide core forms the undercut of the molding article. Hence, the slide core is arranged to be advanced and retracted along the longitudinal direction, and the advanceable and retractable directions are limited to the depth direction of the undercut.
Since the direction of the slide core is limited as stated above, a drive mechanism of the slide core cannot be simplified, and it is difficult to dispose the slide core when the molding article has a part facing the undercut.